In pleated media filter elements, the performance of the filter is enhanced or diminished by the ability of the contaminated fluid to pass freely and completely through the media. If open flow paths are maintained between the pleats, the filter normally operates at its optimum. If, on the other hand, the flow paths through the filter are in some way obstructed or reduced, e.g. when pleats bunch together, the filtering capacity of the media is diminished. Thus, maintaining a certain spacing between successive pleats in a filter element is extremely important to the overall performance of that element. This is especially true of filters having a relatively low pleat density and of filter elements made from non-corrugated media.
In a filter element where pleat density is low, the occurrence of pleat bunching increases as the pressure drop or differential across the filter element increases. This problem increases in severity as the heat and humidity contained within the filter are elevated. When poor pleat spacing occurs in a filter element not only does the pressure drop across a filter increase, but the effective area available for filtration is reduced. The net result is a reduction in the life of the filter caused by the unavailability of the entire filter media for filtration.
Several methods for achieving pre-determined pleat spacing have been devised by others and are known in the art. These include the use of figure eight shaped pleats, the bonding of the pleat tips to the filter liner by using a spiral bead of adhesive, and the use of string, paper or adhesive as a spacer between individual pleats. Also, various methods for corrugating or creating bumps and dimples upon the surfaces of the pleats have been employed in attempts to obtain reliable spacing between filter element pleats.
There are disadvantages however, to all of the above prior art methods. The figure eight pleat arrangement relies upon a pre-determined pleat density to obtain optimum filtration performance. Although the concept of a figure eight pleat was originally intended to achieve self-spacing pleats, such a result has not been consistently and reliably obtained from this method. Figure eight pleat configurations are difficult to obtain at high pleating rates, and the effectiveness of the figure eight pleat is largely negated under conditions of elevated temperature and humidity. Each of the methods of bonding pleat tips to a liner and placing a spacer element between the pleats requires an additional step in the manufacturing process and involves a material add-on which increases the filter construction cost. Forming dimples or bumps which project from the surface of the pleat would initially space the pleats apart, however, during the process of forming such projections the filter media itself is often damaged thereby reducing the effective area available for filtration.
The present invention provides a method for obtaining a unique pleat spacing mechanism which has been tested and found to be reliable for maintaining a given pleat spacing in a filter element, even under conditions of elevated heat and humidity. The present invention can be practiced with a standard pleating machine and at high pleating rates to achieve pleat self-spacing quite efficiently. Furthermore, the recurring disadvantages of the prior art are overcome by the present invention in that the method of practicing the invention requires a minimum of manufacturing steps and there is no need for a material add-on to achieve reliable and dependable spacing between the filter element pleats.